Conclusion

You have now corrected the whole text. Here it is once again, as it should have been written - with the errors corrected, and with alternatives given in brackets.

The universe has been a mystery for many centuries. There are two problems in cosmology. It (This) can be explained with dark matter. Only 10% of matter is known. Missing matter constitutes the other 90 per cent. But it hasn't been found yet. The other problem is the relation between gravity and energy. The universe is in expansion and the more it expands, the more energy it creates. Scientists have a new explanation which could explain both phenomena. In the new theory, dark energy and gravity repulse each other (one another).

POUR APPROFONDIR LES POINTS GRAMMATICAUX ESQUISSES DANS LE COMMENTAIRE, CONSULTEZ LES FICHES GRAMMATICALES DISPONIBLES SUR LE PARCOURS LIBRE.